如何通过列表中的属性值获取/查找对象 [英] How to get/find an object by property value in a list

问题描述

我有一个问题，关于使用LINQ通过搜索"它们的字段名称来获取列表对象.我已经为此编写了简单的Library和Book类:

I have a question about getting a list objects by "searching" their field names using LINQ. I've coded simple Library and Book classes for this:

class Book
{
    public string title { get; private set; }
    public string author { get; private set; }
    public DateTime indexdate { get; private set; }
    public int page { get; private set; }

    public Book(string title,string author, int page)
    {
        this.title = title;
        this.author = author;
        this.page = page;
        this.indexdate = DateTime.Now;
    }
}

class Library
{
    List<Book> books = new List<Book>();

    public void Add(Book book)
    {
        books.Add(book);
    }

    public Book GetBookByAuthor(string search)
    {
        // What to do over here?
    }
}

所以我想获取某些字段等于某些字符串的Book实例，例如

So I want to get Book instances which certain fields is equal to certain strings, like

if(Book[i].Author == "George R.R. Martin") return Book[i];

我知道使用简单的循环代码是可能的，但是我想使用LINQ做到这一点.有什么办法可以做到这一点?

I know it's possible with simple loop codes but I want to do this with LINQ. Is there any way to achieve this?

推荐答案

var myBooks = books.Where(book => book.author == "George R.R. Martin");

并记得添加:using System.Linq;

在您的特定方法中，由于您只想退回一本书，因此您应该写:

In your specific method, since you want to return only one book, you should write:

public Book GetBookByAuthor(string search)
{
    var book = books.Where(book => book.author == search).FirstOrDefault();
    // or simply:
    // var book = books.FirstOrDefault(book => book.author == search);
    return book;
}

Where 返回，然后 FirstOrDefault 返回在可枚举中找到的第一本书；如果未找到，则返回null.

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